The present invention relates to semiconductor optical devices suitable for use in optical communication and to an active region thereof.
Studies have been pursued which change the materials of the multiple-quantum well active layer from the semiconductor materials of InGaAsP-based compounds to the semiconductor materials of InGaAlAs-based compounds to improve high-temperature, high-speed properties in semiconductor lasers for optical communication. This is because the InGaAlAs-based compounds are band-structurally stronger in the confinement of electrons and is little in the degradation of laser properties at high temperatures. On the other hand, in the InGaAlAs-based compounds the crystal surface of the Al-containing layer is subject to oxidation, and so when both sides of the mesa-like active region are buried, defects are generated at the regrowth interface thereof. As a result, although there are the buried structure and the ridge structure as semiconductor laser structures, many InGaAlAs-based semiconductor lasers utilize the ridge type, which does not need the regrowth interface. Examples of InGaAlAs-based lasers include a laser in which the active layer structure uses compressive strain described in claim 1 and FIG. 3 of Japanese Patent Laid-Open No. 10-84170 (patent document 1) and a laser described in Journal of Crystal Growth 145 pp. 858–868, 1994 (non-patent document 1). An example of InGaAlAs-based buried type lasers is one in IPRM 96 ThA2-2 p. 765, 1996 (Intern. Conf. on Indium Phosphide and Related Material; non-patent document 2). In addition, studies of interface treatment in InGaAlAs-based buried type lasers includes a study on sulfur treatment with NH4S; for example, it is known in IPRM98 ThP-48 p. 702, 1998 (Intern. Conf. on Indium Phosphide and Related Material; non-patent document 3). Furthermore, with examples according to lasing wavelengths using compressive strain, for example, there are reported an InGaAs quantum well layer (non-patent document 2) and an InGaAlAs quantum well layer (non-patent document 3), for a 1.55 μm band, and In0.673Ga0.157Al0.17As to In0.75 Ga0.106Al0.143As, etc. for a 1.3 μm band in The 14th International Semiconductor Laser Conference (TH 1.3 p-215, 1994; non-patent document 4).